Ruapehu plane crash: 50 years on

Today marks the 50th anniversary of the tragic Bay of Plenty Airways Aero Commander crash on Mt Ruapehu, en route to Rotorua where family and friends awaited its arrival. The accident and subsequent investigation work is among the most significant and controversial in New Zealand aviation history, as aviation historian Rev Dr Richard Waugh explains.

ON THE morning of November 21, 1961, the sporty looking twin-engined Aero Commander operated by Bay of Plenty Airways was flying scheduled Flight 92 from Wellington to Rotorua and Tauranga.

Its familiar shape and sound was spotted high over the slopes of Mt Ruapehu by several onlookers who saw the tragedy unfold. Roy Turner reported: "When I heard the Aero Commander I looked up as I usually did. Suddenly there was a scream of engine noise and the right wing separated and flew off by itself, the remainder barrel-rolled away with both parts disappearing from sight over the ridge."

Tony Thrupp, working on the chairlifts, commented: "It seemed to be just behind the Pinnacles when I saw a cloud of white smoke appear. Then the right wing fell off and tumbled towards the ground with the engine attached. I heard an engine revving loudly. The plane dived, with flames and smoke pouring from it. After it had dropped out of sight I heard a loud report."

The shocking crash was headline news throughout New Zealand. Many Bay of Plenty people were stunned by the loss of well-known pilot and founder of the airline, Captain Alf Bartlett, aged 36. Passengers killed were Miss Marlene Boynton, aged 25, a midwife returning to Murupara Hospital after a midwifery course in Christchurch; Scottish immigrant Mrs Nicholas Crook, aged 37, also of Murupara, and her young children Jeffrey (2 years) and Helen (8 months); and Mr Irvine Down, aged 41, of Wellington.

Airline beginnings

Bay of Plenty Airways had its beginnings in 1956 with Tauranga Air Services offering local charter flights and eventually regular services. Changing its name to express a wider constituency of support and with the financial backing of New Zealand Newspapers Ltd, the Aero Commander was purchased in the United States and flown the long ferry flight to New Zealand in September 1958 by the airline's driving force, Captain Bartlett, a former RNZAF pilot in World War II.

Scheduled flights using the Aero Commander began on October 11, 1958 between Tauranga, Rotorua and Auckland. The aircraft was kept busy with passengers and freight work. Services later expanded to Whakatane and Wellington.

In the weeks following the Aero Commander crash it was initially thought the airline would continue in a restructured form. However with financial constraints, loss of morale after the accident, and the high cost of new replacement aircraft, Bay of Plenty Airways was placed in liquidation in December 1961.

First accident report

The air accident report was released three months later in February 1962. Despite acknowledged evidence of a substantial fatigue crack in the main spar cap (the load-carrying structure) of the starboard wing, and the complete separation of the wing from the aircraft immediately before the crash, the report blamed Captain Bartlett for the accident.

The report suggested the pilot had flown too close to the summit of Mt Ruapehu, and due either to turbulence or some pilot manoeuvre, the starboard propeller had struck a rock outcrop on the mountain bending the blade tips forward and causing vibration which weakened the wing and led to its rapid failure. The report also stated that "... the structural integrity of the Aero Commander 680S aircraft as a type is unquestioned".

Questions

Professor Neil Mowbray of the University of Auckland became involved in the examination of four photographs taken from a camera used by Irvine Down who was sitting in the front right-hand seat next to Captain Bartlett. The photographs show the approach to Mt Ruapehu, with the last photograph of the crater lake taken only a few seconds before the Aero Commander began to break up in the air. Air accident inspectors contended that the final photograph showed the Aero Commander below the mountain crest but Mowbray determined through photogrammetic analysis that the aircraft was not below the mountain crest at any time.

In 1969, a concerned group of aviation people, led by pilot John Stokes, considered the air accident report unprofessional, and approached Professor Les Erasmus of the Department of Mechanical Engineering at the University of Canterbury for assistance. Professor Erasmus issued a series of reports as different components of the Aero Commander were located and examined, showing that the starboard wing had been defective, and that it could have separated, as a result of metal fatigue, at any time on or around the day of the accident, irrespective of any alleged air turbulence or action by the pilot.

Second report

In 1972, the Chief Inspector of Air Accidents withdrew the original report and issued a new report, which was formalised in January 1984. Although this report accepted some of the new findings, its main thrust was an attempt to justify the errors of the first report, and blame for the accident was still apportioned to the pilot.

Professor Erasmus continued his investigations through the 1970s and 1980s, with the university simulating the propeller impingement of fuselage sections and endeavouring to locate and use similar Aero Commander aircraft for camera angle and depression measurements from the right-hand passenger seat.

New evidence

In essence there are two main areas of disagreement between the second accident report and the findings of Professor Erasmus.

The second accident report suggests one of the surviving photographs shows that the aircraft turned to starboard and dived at the crater lake. As the pilot pulled out of the dive the starboard propeller struck snow only, bending the blade tips forward, but leaving no other damage. Then as the severed wing passed rearwards the corresponding part of each blade struck the horizontal stabiliser, producing the observed metal to metal contact.

By comparing photographs taken from the right-hand seat of test aircraft with the last one taken from the ill-fated Aero Commander, Professor Erasmus was able to show that the camera depression and starboard rotation correspond to camera movement only, and that the aircraft's orientation was largely unchanged from its previous route when the photograph was taken.

In their reports the accident inspectors were not prepared to concede that the propeller blade tips would be bent forward as a result of the propeller striking the fuselage when the starboard wing pivoted forward during wing failure. This is despite mathematical (vector diagram) proof given in Prof Erasmus' reports. Also, the accident inspectors could not accept that an aircraft of this type might have a major design weakness which would initiate a fatigue crack in the wing spar.

Australian research

In May 1995 Mr Steve Swift, principal engineer Fatigue Evaluation, Civil Aviation Authority of Australia, presented an extensive paper, The Aero Commander Chronicle, summarising the history of the Aero Commander design and the difficult lessons learned in the theory and practice of fatigue control. The paper reports 24 Aero Commander accidents resulting from wing separation in flight, worldwide, of which Bay of Plenty Airways ZK-BWA was the first. The report further relates how 35 wing spars had been found cracked during inspection, many requiring replacement of the spar caps. Fortunately Aero Commanders now fly safely, despite the design weakness, because better inspections find cracks early, before they become dangerous.

Intransigence

The second aircraft accident report of 1984 continues to perpetuate an injustice on the circumstances of the Bay of Plenty Airways accident, especially the reputation of Captain Bartlett. Aircraft engineer Denis Little, provides a helpful word on this air accident when he reflected: "It is never too late to learn from past mistakes, nor should there be any shame in acknowledging them".

A 50th anniversary service with a plaque and display unveiling will be held at Tauranga's Classic Flyers Museum today. Lectures on the airline and accident investigation were to be given by Dr Waugh, Professor Erasmus and Steve Swift.